1. Field of the Invention
The invention relates to means and a process for making straight cuts, curved cuts and combinations thereof through a continuously moving web, and more particularly to such a means and a process capable of making such cuts in thin, pliable, compliant, cut-resistant plastic and/or fibrous material.
2. Description of the Prior Art
Prior art workers have devised numerous types of rotary shears. One well known construction involves the use of a sharp disc-like blade and a rigid backup cylinder, producing a typical crush cut in a web of material. Another approach involves the use of two cooperating blades. A typical two-blade rotary shear is taught, for example, in U.S. Pat. No. 3,956,957 in the name of Louis Corse, issued May 18, 1976.
U.S. Pat. No. 559,179 in the name of Herman I. Koegel, issued Apr. 28, 1896 and U.S. Pat. No. 668,945 in the name of Aaron Allen, issued Feb. 26, 1901 teach rotary shears for cutting paper webs utilizing cooperating pairs of disc or dish-shaped blades located at a slight angle with respect to each other in order to provide single-point contact therebetween. The last mentioned reference also teaches spring loading one of the disc-like blades against the other.
U.S. Pat. No. 1,063,298 in the name of Henry C. Smith, issued June 3, 1913 and U.S. Pat. No. 3,364,701 in the name of George S. Rouyer and Marcel Duchemin, issued Jan. 23, 1968 set forth rotary shear-like apparatus employing specially configured blade elements for the cutting of sheet metal.
Finally, U.S. Pat. No. 3,459,086 in the name of George E. Reeder, Jr., issued Aug. 5, 1969 and U.S. Pat. No. 3,682,032 in the name of John D. Pfeiffer, issued Aug. 8, 1972 teach rotary shear or slitter apparatus for webs of paper and the like utilizing cooperating pairs of disc-like blades skewed with respect to each other so as to have a point contact therebetween. In both of these last mentioned references, the disc-like blades are specially configured to increase the life of their cutting edges.
While the rotary shear of the present invention may have many applications, it is particularly adapted to the formation of straight and curved cuts, and combinations thereof, at high cutting speeds through a continuously moving web of thin, pliable, compliant, cut-resistant material.
As a non-limiting example of such a web, reference is made to U.S. Letters Pat. No. 3,860,003 which teaches a disposable diaper construction wherein the diaper is made up of three basic parts: a flexible, moisture impermeable back sheet, an absorbent core and a porous, fibrous top sheet. The back sheet may be made of such material as low density, opaque polyethylene. The top sheet may be made of material such as woven or non-woven mixtures of small denier polyester and rayon fibers. The back sheet and top sheet are joined directly together at the diaper edges. In the usual mode of manufacture, the disposable diapers are formed in a continuous web which is ultimately severed into the individual diaper product. Each diaper, along its longitudinal edges, is provided with elongated notches so that the diaper is in part preformed. These longitudinal edge notches are preferably cut while the diapers are still in the form of a continuous web.
Unlike paper and metal structures which behave more or less like rigid bodies during a shearing operation, a thin, pliable, compliant web, such as that constituting the back and top sheets of the above described diaper structure, resists conventional shearing due to the compliant nature of the web, its tendency to bend, its small caliper which passes through any gaps in blade contact, the presence of small denier fibers difficult to cut and the basic cut resistance of a tough plastic-like polyester.
For purposes of an exemplary showing, the high-speed rotary shear and the process of the present invention will be described in terms of the formation of longitudinal edge notches in a web of disposable diaper material. The high-speed rotary shear and the shearing process are capable of producing straight cuts (parallel to or at an angle to the direction of web movement), curved cuts and combinations thereof in a web of such compliant material with a true shearing action similar to that produced by a pair of scissors or shears. Just what constitutes "high-speed" depends, of course, on the material being cut and the complexity of the cuts being made. In the embodiment described with the difficulty cut web described, the term "high speed" is intended to refer to a web speed of from about 200 to about 600 feet per minute or more. The rotary shear is provided with a blade arrangement wherein light weight blades are affixed at the periphery of disc-like or cylindrical blade supports and at least one of the blades is in part at least elastically mounted and is itself flexible. This provides a much lower blade inertia in use (as opposed to the use of a disc-like blade or the like), and enables the obtaining of the quick response necessary to provide a sharp, non-linear, clean and complete cut at regularly spaced intervals along the length of a rapidly moving compliant web having a low coeffecient of friction and which does not provide the rigid effect during the shearing operation as does paper, metal or the like. Inertia, of less importance in low speed devices, is of great importance in a high speed rotary shear of the type herein contemplated in the maintenance of single point contact between cooperating blades throughout each cut and to prevent dancing or bouncing of the blades which would preclude the obtaining of clean and complete cuts. Finally, the blade structures of the present invention demonstrate excellent working life and may be readily and easily replaced when required.